George T. Jefferson and Lowell Lindsay, eds. FOSSIL TREASURES OF THE ANZA-BORREGO DESERT—THE LAST SEVEN YEARS. Sunbelt Publications; 416 pgs; $49.95.

Larry McCaffery

[NOTE: The following originally appeared at the lead review of the SAN DIEGO UNION BOOK REVIEW in 2006.]

Other than the howls of coyotes and the occasional sound of tires moving across lonely highways, this landscape is today mostly silent. But listen more carefully: within Anza-Borrego’s badlands lie some 6000 meters of exposed, fossil-bearing sediments (by way of contrast, the Grand Canyon’s exposures are only 1/3 as great); these deposits, which have accumulated during the past 7 millions years or so, have a grand and utterly improbable story to tell about a period when Anza-Borrego was not a desert but a verdant environment of rivers and floodplains, lakes, forest, and savannah; for several million years this region supported a bestiary of exotic flora and fauna that reads like a “Who’s Who” of unique North American creatures, including the largest known mammoths, saber toothed cats, iguanas, jaguars, giant tortoises and short-faced bears, dwarf pronghorns, flamingos, ground sloths, zebras, camels, and the largest flying bird of the northern hemisphere (“Aiolornis incredibilis”), with a 16 foot wingspan.

This story—told in the secret language of leaf impressions, bone and shell fragments, teeth, and animal tracks—is magnificently recounted in George T. Jefferson and Lowell Lindsay’s landmark new study, “Fossil Treasures of the Anza Borrego Desert.” Unfolding as a series of 20 chapters written by paleontologists and geologists from across the U.S., and supplemented by several hundred color photographs, exquisite illustrations, and 2-page paleolandscapes that help bring the past to life throughout, “Fossil Treasures” offers both specialists and ordinary readers an embarrassments of riches

Clustered near the beginning and end of the volume are several chapters that set the stage for the paleontological drama that follows by summarizing the region’s geology and climate, its history of fossil research, and providing background about the nature of fossil collecting, stratigraphic dating, intercontinental connections, and other topics that help explain how and why these fossils came to exist where they did.

The remaining chapters explore the fossilized remains of the creatures themselves that have been uncovered from over 250 localities in the Park. These fossils include more than 550 types of plants and animals—most of them extinct and some only known from remains recovered in the Park—ranging from preserved microscopic plant pollen and algal spores to mammoth and baleen whale bones.

These fossils are discussed in their natural order, beginning with the invertebrate fossils (corals, mollusks, crustaceans, and echinoderms) of the ancient Imperial Sea (the proto-Gulf of California, which 7 million years ago reached as far north as the San Gregorio Pass near Palm Springs), and continuing on through the lower vertebrates (fish, amphibians, and reptiles), birds, small and large carnivores (wolves, bears, saber toothed cats), and concluding with the region’s most famous fossils—those of the “megaforms” such as camels, horses, and mammoths.

The “back story” chapters make for some of the most interesting reading in the entire volume. Along the way readers are treated to dozens of subplots on such topics as how the Grand Canyon sediments wound up in Anza-Borrego, the evolution of horns and teeth, the role that camels played in the American southwest during the 19th century, the role that changes in the earth’s polarity and ash from volcanic super-explosions several hundred miles away have played in dating Borrego’s fossils, and continental connections that allowed two-way migrations of terrestrial animals across the Isthmus of Panama starting some 3.5 million years ago, as well as across the Bering Land Bridge during the Ice Ages.
Equally fascinating is the volume’s first chapter, Barbara Marrs’ “The History of Anza-Borrego Desert State Park’s Fossil Collections.” Marrs opens this lively overview by quoting from several diary entries that recount the sense of puzzled amazement expressed by early explorers of the Colorado Desert when they discovered evidence that an enormous inland lake once existed in the parched, sweltering environment they were encountering. She then summarizes the gradual build-up of scientific interest in the region, beginning with the extensive collection of invertebrate fossils during the early decades of the 20th century. Soon after the establishment of Anza-Borrego State Park in the early 1930s, a new phase in Borrego’s growing reputation as a major fossil cite was ushered in with the discovery of mammalian fossils. By the mid-50s, it had gradually become clear that scientists were observing a paleontological phenomenon that was unparalleled in North America: “thousands of feet of thick layers of fresh water sediments that had been laid down in a conformable (unbroken) biochronological sequence, which contained a practically perfect record of vertebrate fossil fauna spanning a time of no less than 2.5 million years.” Marrs then takes us up to more recent field world, including George Miller’s acclaimed discovery in 1986 of the most complete skeleton of “Mammoths meridionalis” (southern mammoth) found in North America.
Arising out of the 20 individual chapters are several major themes—adaptation, evolution, extinction, and the influence of changing environments on animals and the landscapes—that provide an overall structural unity to the array of topics raised here. Co-editors Jefferson and Lindsay are well aware that providing a means for comprehending the nature and origin of this fossil record is enormously challenging. And it is certainly to their credit that they have not only done a superb job in gathering together a world-class, state-of-the-art collection of essays, but that they have done so in a manner that combines scientific accuracy with readability. To assist readers who are, like myself, paleontologically-challenged, they have also provided additional materials, including glossaries, tables, appendices, color-coded charts and maps, dozens of exquisite drawings, and hundreds of color photographs. But what works best of all in terms of bringing these fossil creatures and the landscapes they originally inhabited back to life are the series of 5 stunning, 2-page, full color paleolandscapes created by John Francis) that depict the story’s major episodes and habitats.
As the first comprehensive treatment of Anza-Borrego’s fabulous fossil record, “Fossil Treasures,” contains enough raw data and unsolved mysteries to keep scientists busy for the next 7 million years (by then, of course, Borrego will have been transformed into an entirely new landscape). In the meantime, it’s the simple principle of juxtaposition—the mind-boggling contrast between the arid Anza-Borrego Desert of today and the lush landscape teeming with life that existed a few million years ago—that makes “Fossil Treasures” such a challenging and endlessly fascinating read.

.
EXCERPT

During the Pliocene and Pleistocene Epochs of geologic time, when ground sloths, camels, mammoths, and other large, bizarre, and now-extinct animals roamed Anza-Borrego, the environment was very different from the desert setting we see today. Climatic and geologic conditions prevailing then sometimes permitted the remains of these animals to be deposited where they lay, relatively protected from the elements, under mud or sand, in places that allowed them to be partially transformed into fossils over the millennia. All the protein and other soluble organic materials contained in living bone decayed and dissolved away, leaving only its mineral matrix, a substance quite brittle all by itself. The fragile bits of vertebrae, skulls, teeth, limb bones, and jawbones found in Anza-Borrego are generally more delicate than the rock strata in which they are embedded; they usually have not been hardened, as have fossils from many other settings, by exposure to minerals dissolved in the groundwater.
Although nearly all Anza-Borrego vertebrate fossils are shattered fragments, chipped and cracked, they are an unparalleled collection of past life. Recovered as they weathered out of the hills and washes, identified, catalogued and held in labeled trays, steel cabinets, and display cases, these fossils in their thousands tell a more complete and continuous story of vertebrate life than those from any other site of comparable age in North America. They have always captivated Park visitors, many of whom ask, “How old are the bones?” This question is easy to phrase but difficult to answer. After all, how do we know what we know?
—From Paul Remeika, “Dating, Ashes, and Megnetics: New Times for Old Bones”

CONTRIBUTOR’S NOTE:

Larry McCaffery’s most recent book is EXPELLED FROM EDEN: A WILLIAM T. VOLLMANN READER (Thunder’s Mouth Press). A Professor of English at SDSU, he currently lives in Anza Borrego’s magnificent desolation with his wife, Sinda Gregory.